The amino acid composition and sequence of cyanogen bromide peptides obtained from homogeneous cytochrome c peroxidase will be described in sufficient detail to facilitate interpretation of the electron density map of this protein which has been obtained by Prof. Joseph Kraut at UCSD. Analogs of peptide 66-104 of cytochrome c containing a single amino acid replacement at position 81 are being synthesized by Dr. Leon Barstow at the University of Arizona. These peptides will be covalently coupled with hemepeptide 1-65 to reconstitute cytochromes c useful in demonstrating the role of its exposed heme edge in protein: protein complexation and electron exchange. Finally, a computer program will be developed to predict the most likely mode of complexation of cytochrome c and cytochrome c peroxidase.